This invention concerns a method of coating metal substrates with alloys at a substrate temperature above 500.degree. C., preferably between 800.degree. C. and 1100.degree. C.
It is known to heat substrates to temperatures which are considerably above room temperature, for the purpose, for example, of increasing the strength of adhesion between the base metal forming the substrate and the vacuum deposited coating by intermetallic diffusion. Hitherto the effort has been made to keep the substrate temperature at a level as uniform as possible throughout the vacuum depositing process.
In the vacuum depositing of oxidation-inhibiting and corrosion-inhibiting surface coatings on gas turbine blades coating thicknesses of an order of magnitude between 150 and 400.times.10.sup.-3 mm have been necessary on account of the stability required. In the formation of such coatings from special CoCrAlY and NiCoCrAlY alloys suitable for the specified purpose, however, it has been found that seams and fringed crystals form in the coatings and partially nullify the protective qualities of the coating.